Pulse output circuit, shift register, and display device

ABSTRACT

An object is to suppress change of a threshold voltage of a transistor in a shift register and to prevent the transistor from malfunctioning during a non-selection period. A pulse output circuit provided in the shift register regularly supplies a potential to a gate electrode of a transistor which is in a floating state so that the gate electrode is turned on during a non-selection period when a pulse is not outputted. In addition, supply of a potential to the gate electrode of the transistor is performed by turning on or off another transistor regularly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/949,371, filed Jul. 24, 2013, now allowed, which is a continuation ofU.S. application Ser. No. 13/093,002, filed Apr. 25, 2011, now U.S. Pat.No. 8,508,459, which is a continuation of U.S. application Ser. No.11/871,704, filed Oct. 12, 2007, now U.S. Pat. No. 7,932,888, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2006-282931 on Oct. 17, 2006, all of which are incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pulse output circuit, a shiftregister, and a display device, a semiconductor device, and anelectronic device each of the devices having the shift register,particularly relates to a pulse output circuit, a shift register, and adisplay device, a semiconductor device, and an electronic device eachhaving a thin film transistor (TFT) having one conductivity type.

2. Description of the Related Art

In recent years, a display device in which a circuit is formed using athin film transistor (hereinafter also referred to as a TFT) that isformed using a semiconductor thin film over an insulator, particularlyover a glass substrate or a plastic substrate has been developed,particularly an active matrix display device has been developed. Anactive matrix display device formed by using a TFT has several hundredsof thousands to several millions of pixels which are arranged in matrix,and an image is displayed by controlling the charge of each pixel withthe TFT arranged in each pixel.

In addition, as a recent technique, a method in which a driver circuitis formed by using a TFT in the peripheral region of a pixel portion atthe same time as a pixel TFT which forms a pixel has been developed.Such a method contributes greatly to reduction in the size and weightand low power consumption of a device, and along with this, a TFT is anessential device for a display portion and the like of a mobileinformation terminal of which an applicable field has been significantlyexpanded in recent years.

In general, as a circuit which forms a driver circuit of a displaydevice, a CMOS circuit in which an N-channel TFT and a P-channel TFT arecombined is used. As features of the CMOS circuit, the following can begiven: one feature is that power consumption in the whole circuit can besuppressed to a very low level because current flows only at the momentwhen a logic is changed (from an H (High) level to an L (Low) level, orfrom an L level to an H level) and current does not flow ideally(actually, there is minute leakage current) while a certain logic isheld, and another feature is that high speed operation is possiblebecause TFTs having different polarities operate complementarily.

However, in consideration of manufacturing steps, since an ion dopingprocess or the like of the CMOS circuit is complicated, a large numberof manufacturing steps have an effect on production cost directly. Thus,a circuit is proposed, which is formed using a unipolar TFT that iseither an N-channel TFT or a P-channel TFT instead of a CMOS circuitthat is conventionally used, and which achieves high speed operationequivalent to the CMOS circuit (e.g., refer to Reference 1: JapanesePublished Patent Application No. 2002-335153).

As shown in FIGS. 7A to 7C, in a circuit described in Reference 1, whena gate electrode of a TFT 2050 which is electrically connected to anoutput terminal is made to be in a floating state temporarily, apotential of the gate electrode can be set as a potential which ishigher than a power supply potential by using capacitive couplingbetween the gate and a source of the TFT 2050. As a result, an outputwithout amplitude attenuation can be obtained without generating avoltage drop due to a threshold value of the TFT 2050. Referencenumerals 2010, 2020, 2030, 2040, and 2060 are TFTs. Reference numeral2070 is a capacitor. Reference numeral 2100 is a first amplitudecompensation circuit and reference numeral 2200 is a second amplitudecompensation circuit.

Such operation in the TFT 2050 is referred to as bootstrap operation.With this operation, an output pulse can be obtained without generatinga voltage drop due to the threshold value of the TFT.

In addition, in the circuit illustrated in FIGS. 7A to 7C, both gateelectrodes of the TFT 2050 and a TFT 2060 are in a floating state duringthe period when there is no input and output of a pulse, so that apotential change, such as noise, occurs in a node a. However, in orderto solve this problem, a circuit (see FIGS. 8A to 8C) is proposed inwhich noise generated in the node α is reduced when a TFT 1020 and a TFT1060 are turned on and are in a floating state during the period whenthere is no input and output of a pulse (e.g., see Reference 2: JapanesePublished Patent Application No. 2004-226429). Reference numerals 1010,1030, 1040, and 1050 are TFTs. Reference numeral 1070 is a capacitor.Reference numeral 1100 is a first amplitude compensation circuit andreference numeral 1200 is a second amplitude compensation circuit.

SUMMARY OF THE INVENTION

In FIGS. 8A to 8C, when attention is focused on an SROut1, CK1 variesfrom an H level to an L level after a pulse is outputted. Along withthis, a potential of the SROut1 begins to decrease. On the other hand, asimilar operation to the above-described operation is also performed ina second stage at timing when CK2 becomes an H level, and a pulse isoutputted to an SROut2. This pulse is inputted to an input terminal 3 ina first stage, and a TFT 1030 is turned on. Accordingly, potentials ofgate electrodes of the TFT 1020 and the TFT 1060 increase and the TFT1020 and the TFT 1060 are turned on. Along with this, a potential of agate electrode of a TFT 1050 and a potential of the SROut1 decrease.Then, when an output of the SROut2 changes from an H level to an Llevel, the TFT 1030 is turned off. Accordingly, the gate electrodes ofthe TFT 1020 and the TFT 1060 are in a floating state at this moment.After that, this state continues until the next SP is inputted in thefirst stage.

In this way, in the circuit of FIGS. 8A and 8B, a node β is in afloating state during the period when there is no input and output of apulse. For example, in the case where the circuit of FIGS. 8A and 8B isused as a scan driver, a potential of the node β needs to be held duringabout one frame. Since channel widths of a TFT 1040 and the TFT 1060relatively increase, off-current also increases. At this time, thepotential of the node β may decrease due to the off-current of the TFT1040 and the TFT 1060, and the TFT 1060 may be turned off in some cases.As a result, a circuit has a possibility of malfunction due tocapacitive coupling with a clock signal.

In addition, when a pulse is outputted from the TFT 1050, the node β isin a floating state. Therefore, when a potential of a node γ rises froman L level to an H level, the potential of the node β increases due tocapacitive coupling in some cases. As a result of this, there is apossibility that the TFT 1020 may be turned on and malfunction mayoccur. Since this potential change is much smaller than normal pulseamplitude, this potential change does not become a problem as long asthe potential change is smaller than a threshold value of the TFT 1020.However, when the potential change is larger than the threshold value ofthe TFT 1020, malfunction may occur because the potential of the node αdecreases. In particular, when amorphous silicon is used for a TFT, anitride film is often used as a gate insulating film, and a thresholdvalue changes in some cases. As a result of this, there is a highpossibility that a pulse output circuit may malfunction.

When amorphous silicon is used for a TFT, compared with a TFT usingpolysilicon, sufficient drive capability is difficult to be obtainedbecause of inferior electric characteristics and a threshold valueshifts due to a voltage condition. Accordingly, a problem is a circuittechnique to form a driver circuit which drives a pixel by using a TFTwhich uses amorphous silicon.

An object of the present invention disclosed in this specification is toprovide a pulse output circuit, a shift register, and a display deviceeach of which reduces malfunction in a circuit and assures furtherreliable operation by solving one or a plurality of such problems.

A pulse output circuit of the present invention regularly supplies apotential to a gate electrode of a transistor which is in a floatingstate so that the gate electrode is turned on during a non-selectionperiod when a pulse is not outputted. In addition, supply of a potentialto the gate electrode of the transistor is performed by turning on oroff another transistor regularly.

In addition, a shift register of the present invention is driven so thata pulse outputted from an m-th pulse output circuit overlaps half (½period) of a pulse outputted from a (m+1)th pulse output circuit.Hereinafter, specific structures of the shift register and the pulseoutput circuit of the present invention will be described.

A shift register of the present invention includes a plurality of pulseoutput circuits including at least a (m−2)th pulse output circuit, a(m−1)th pulse output circuit, an m-th pulse output circuit, a (m+1)thpulse output circuit, and a (m+2)th pulse output circuit (m≧3); andfirst to fourth signal lines each of which outputs a clock signal, inwhich each of the pulse output circuits includes first to sixth inputterminals and an output terminal; the first to third input terminals ofthe m-th pulse output circuit are electrically connected to any of thefirst to fourth signal lines; the fourth input terminal of the m-thpulse output circuit is electrically connected to the output terminal ofthe (m−2)th pulse output circuit; the fifth input terminal of the m-thpulse output circuit is electrically connected to the output terminal ofthe (m−1)th pulse output circuit; the sixth input terminal of the m-thpulse output circuit is electrically connected to the output terminal ofthe (m+2)th pulse output circuit; and the output terminal of the m-thpulse output circuit is electrically connected to the sixth inputterminal of the (m−2)th pulse output circuit, the fifth input terminalof the (m+1)th pulse output circuit, and the fourth input terminal ofthe (m+2)th pulse output circuit.

A pulse output circuit of the present invention includes first to ninthtransistors, in which a first electrode of the first transistor iselectrically connected to a first power supply line, a second electrodeof the first transistor is electrically connected to a gate electrode ofthe third transistor, and a gate electrode of the first transistor iselectrically connected to a fourth input terminal; a first electrode ofthe second transistor is electrically connected to a second power supplyline, a second electrode of the second transistor is electricallyconnected to the gate electrode of the third transistor, and a gateelectrode of the second transistor is electrically connected to a gateelectrode of the fourth transistor; a first electrode of the thirdtransistor is electrically connected to a first input terminal and asecond electrode of the third transistor is electrically connected to anoutput terminal; a first electrode of the fourth transistor iselectrically connected to a third power supply line and a secondelectrode of the fourth transistor is electrically connected to theoutput terminal; a first electrode of the fifth transistor iselectrically connected to a fourth power supply line, a second electrodeof the fifth transistor is electrically connected to the gate electrodeof the second transistor and the gate electrode of the fourthtransistor, and a gate electrode of the fifth transistor is electricallyconnected to the fourth input terminal; a first electrode of the sixthtransistor is electrically connected to the fourth power supply line, asecond electrode of the sixth transistor is electrically connected tothe gate electrode of the second transistor and the gate electrode ofthe fourth transistor, and a gate electrode of the sixth transistor iselectrically connected to a fifth input terminal; a first electrode ofthe seventh transistor is electrically connected to a fifth power supplyline, a second electrode of the seventh transistor is electricallyconnected to the gate electrode of the second transistor and the gateelectrode of the fourth transistor, and a gate electrode of the seventhtransistor is electrically connected to a sixth input terminal; a firstelectrode of the eighth transistor is electrically connected to thefifth power supply line, a second electrode of the eighth transistor iselectrically connected to a second electrode of the ninth transistor,and a gate electrode of the eighth transistor is electrically connectedto a second input terminal; and a first electrode of the ninthtransistor is electrically connected to the gate electrode of the secondtransistor and the gate electrode of the fourth transistor, and a gateelectrode of the ninth transistor is electrically connected to a thirdinput terminal.

A display device of the present invention includes a pixel; and a shiftregister to drive the pixel, in which the shift register includes aplurality of pulse output circuits including at least a (m−2)th pulseoutput circuit, a (m−1)th pulse output circuit, an m-th pulse outputcircuit, a (m+1)th pulse output circuit, and a (m+2)th pulse outputcircuit (m≧3); and first to fourth signal lines each of which outputs aclock signal, and each of the pulse output circuits includes first tosixth input terminals and an output terminal; the first to third inputterminals of the m-th pulse output circuit are electrically connected toany of the first to fourth signal lines; the fourth input terminal ofthe m-th pulse output circuit is electrically connected to the outputterminal of the (m−2)th pulse output circuit; the fifth input terminalof the m-th pulse output circuit is electrically connected to the outputterminal of the (m−1)th pulse output circuit; the sixth input terminalof the m-th pulse output circuit is electrically connected to the outputterminal of the (m+2)th pulse output circuit; and the output terminal ofthe m-th pulse output circuit is electrically connected to the sixthinput terminal of the (m−2)th pulse output circuit, the fifth inputterminal of the (m+1)th pulse output circuit, and the fourth inputterminal of the (m+2)th pulse output circuit.

In accordance with the present invention, by regularly supplying apotential to a gate electrode of a transistor which is in a floatingstate during a non-selection period when an input and output of a pulseis not performed, malfunction of a pulse output circuit can besuppressed.

In addition, by using a driving method in which a pulse outputted fromthe m-th pulse output circuit overlaps half (½ period) of a pulseoutputted from the (m+1)th pulse output circuit, the present inventioncan provide a pulse output circuit which can withstand large load andoperate at high frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing an example of a shift register of thepresent invention, and FIGS. 1B and 1C are diagrams each showing anexample of a pulse output circuit of the present invention.

FIG. 2 is a diagram showing an operation example of a pulse outputcircuit of the present invention.

FIGS. 3A to 3D are diagrams each showing an operation example of a pulseoutput circuit of the present invention.

FIGS. 4A to 4D are diagrams each showing an operation example of a pulseoutput circuit of the present invention.

FIG. 5A is a diagram showing operation of a pulse output circuit of thepresent invention, and FIG. 5B is a diagram showing operation of aconventional pulse output circuit, which are compared with each other.

FIG. 6A is a diagram showing an example of a shift register of thepresent invention, and FIGS. 6B and 6C are diagrams each showing anexample of a pulse output circuit of the present invention.

FIG. 7A is a diagram showing an example of a conventional shiftregister, FIG. 7B is a diagram showing an example of a conventionalpulse output circuit, and FIG. 7C is a diagram showing an example ofoperation of the conventional pulse output circuit.

FIG. 8A is a diagram showing an example of a conventional shiftregister, FIG. 8B is a diagram showing an example of a conventionalpulse output circuit, and FIG. 8C is a diagram showing an example ofoperation of the conventional pulse output circuit.

FIGS. 9A to 9C are diagrams each showing an example of a display deviceprovided with a shift register of the present invention.

FIGS. 10A and 10B are diagrams each showing an example of a displaydevice provided with a shift register of the present invention.

FIGS. 11A and 11B are diagrams each showing an example of a displaydevice provided with a shift register of the present invention.

FIGS. 12A to 12C are diagrams each showing an example of a displaydevice provided with a shift register of the present invention.

FIG. 13 is a diagram showing an example of a display device providedwith a shift register of the present invention.

FIGS. 14A to 14H are diagrams each showing an example of an electronicdevice provided with a shift register of the present invention.

FIGS. 15A and 15B are diagrams each showing an example of a displayelement of a display device provided with a shift register of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes of the present invention will be describedwith reference to the accompanying drawings. However, the presentinvention can be implemented in various modes. As can be easilyunderstood by a person skilled in the art, the modes and details of thepresent invention can be changed in various ways without departing fromthe spirit and scope of the present invention. Thus, the presentinvention should not be interpreted as being limited to the followingdescription of the embodiment modes. Note that the same referencenumeral is commonly used to denote the same component among differentdrawings in structures of the present invention explained below.

(Embodiment Mode 1)

In this embodiment mode, an example of a pulse output circuit of thepresent invention and a shift register including the pulse outputcircuit will be described with reference to drawings.

A shift register shown in this embodiment mode includes first to n-thpulse output circuits 10 _(—1) to 10 _(—n) (n≧3) and first to fourthsignal lines 11 to 14 each of which outputs a clock signal (see FIG.1A). The first signal line 11 outputs a first clock signal (CK1), thesecond signal line 12 outputs a second clock signal (CK2), the thirdsignal line 13 outputs a third clock signal (CK3), and the fourth signalline 14 outputs a fourth clock signal (CK4).

The clock signals (CK) are signals which alternate between an H (High)signal and an L (Low) signal at a regular interval, and here, the firstto fourth clock signals (CK1) to (CK4) are delayed for ½ periodsequentially. In this embodiment mode, by using the first to fourthclock signals (CK1) to (CK4), control or the like of driving of a pulseoutput circuit is performed.

Each of the first to n-th pulse output circuits 10 _(—1) to 10 _(—n)includes a first input terminal 21, a second input terminal 22, a thirdinput terminal 23, a fourth input terminal 24, a fifth input terminal25, a sixth input terminal 26, and an output terminal 27 (see FIG. 1B).

The first input terminal 21, the second input terminal 22, and the thirdinput terminal 23 are electrically connected to any of the first tofourth signal lines 11 to 14. For example, in FIGS. 1A to 1C, the firstinput terminal 21 of the first pulse output circuit 10 _(—1) iselectrically connected to the first signal line 11, the second inputterminal 22 of the first pulse output circuit 10 _(—1) is electricallyconnected to the second signal line 12, and the third input terminal 23of the first pulse output circuit 10 _(—1) is electrically connected tothe third signal line 13. In addition, the first input terminal 21 ofthe second pulse output circuit 10 _(—2) is electrically connected tothe second signal line 12, the second input terminal 22 of the secondpulse output circuit 10 _(—2) is electrically connected to the thirdsignal line 13, and the third input terminal 23 of the second pulseoutput circuit 10 _(—2) is electrically connected to the fourth signalline 14.

In the m-th pulse output circuit (m≧3) of the shift register shown inthis embodiment mode, the fourth input terminal 24 of the m-th pulseoutput circuit is electrically connected to the output terminal 27 ofthe (m−2)th pulse output circuit and the fifth input terminal 25 of the(m−1)th pulse output circuit. The fifth input terminal 25 of the m-thpulse output circuit is electrically connected to the output terminal 27of the (m−1)th pulse output circuit and the fourth input terminal 24 ofthe (m+1)th pulse output circuit. The sixth input terminal 26 of them-th pulse output circuit is electrically connected to the outputterminal 27 of the (m+2)th pulse output circuit. The output terminal 27of the m-th pulse output circuit is electrically connected to the sixthinput terminal 26 of the (m−2)th pulse output circuit, the fifth inputterminal 25 of the (m+1)th pulse output circuit, and the fourth inputterminal 24 of the (m+2)th pulse output circuit, and outputs a signal toOUT(m).

For example, in the third pulse output circuit 10 _(—3), the fourthinput terminal 24 is electrically connected to the output terminal ofthe first pulse output circuit 10 _(—1) and the fifth input terminal ofthe second pulse output circuit 10 _(—2). The fifth input terminal 25 ofthe third pulse output circuit 10 _(—3) is electrically connected to theoutput terminal of the second pulse output circuit 10 _(—2) and thefourth input terminal of the fourth pulse output circuit 10 _(—4). Thesixth input terminal 26 of the third pulse output circuit 10 _(—3) iselectrically connected to the output terminal of the fifth pulse outputcircuit 10 _(—5). The output terminal of the third pulse output circuit10 _(—3) is electrically connected to the sixth input terminal of thefirst pulse output circuit 10 _(—1), the fifth input terminal of thefourth pulse output circuit 10 _(—4), and the fourth input terminal ofthe fifth pulse output circuit 10 _(—5). In addition, in the third pulseoutput circuit 10 _(—3), a signal outputted from the output terminal ofthe first pulse output circuit 10 _(—1) is inputted to the fourth inputterminal 24 of the third pulse output circuit 10 _(—3). A signaloutputted from the output terminal of the second pulse output circuit 10_(—2) is inputted to the fifth input terminal 25 of the third pulseoutput circuit 10 _(—3). A signal outputted from the output terminal ofthe fifth pulse output circuit 10 _(—5) is inputted to the sixth inputterminal 26 of the third pulse output circuit 10 _(—3). A signaloutputted from the output terminal 27 of the third pulse output circuit10 _(—3) is inputted to the sixth input terminal of the first pulseoutput circuit 10 _(—1), the fifth input terminal of the fourth pulseoutput circuit 10 _(—4), and the fourth input terminal of the fifthpulse output circuit 10 _(—5).

In addition, a first start pulse (SP1) is inputted to the fourth inputterminal 24 of the first pulse output circuit, and a second start pulse(SP2) is inputted to the fifth input terminal 25 of the first pulseoutput circuit.

Next, a specific structure of each of the first to n-th pulse outputcircuits 10 _(—1) to 10 _(—n) will be described.

Each of the first to n-th pulse output circuits 10 _(—1) to 10 _(—n)includes first to ninth transistors 101 to 109, a first capacitor 111,and a second capacitor 112 (see FIG. 1C). Further, signals are suppliedto the first to ninth transistors 101 to 109 from first to sixth powersupply lines 31 to 36, in addition to the first to sixth input terminals21 to 26 and the output terminal 27.

A first electrode (either one of a source electrode or a drainelectrode) of the first transistor 101 is electrically connected to thefirst power supply line 31, a second electrode (the other one of thesource electrode or the drain electrode) of the first transistor 101 iselectrically connected to a gate electrode of the third transistor 103and a second electrode of the second capacitor 112, and a gate electrodeof the first transistor 101 is electrically connected to the fourthinput terminal 24. A first electrode of the second transistor 102 iselectrically connected to the second power supply line 32, a secondelectrode of the second transistor 102 is electrically connected to thegate electrode of the third transistor 103, and a gate electrode of thesecond transistor 102 is electrically connected to a gate electrode ofthe fourth transistor 104. A first electrode of the third transistor 103is electrically connected to the first input terminal 21, and a secondelectrode of the third transistor 103 is electrically connected to theoutput terminal 27. A first electrode of the fourth transistor 104 iselectrically connected to the third power supply line 33, and a secondelectrode of the fourth transistor 104 is electrically connected to theoutput terminal 27. A first electrode of the fifth transistor 105 iselectrically connected to the fourth power supply line 34, a secondelectrode of the fifth transistor 105 is electrically connected to thegate electrode of the second transistor 102 and the gate electrode ofthe fourth transistor 104, and a gate electrode of the fifth transistor105 is electrically connected to the fourth input terminal 24. A firstelectrode of the sixth transistor 106 is electrically connected to thefourth power supply line 34, a second electrode of the sixth transistor106 is electrically connected to the gate electrode of the secondtransistor 102 and the gate electrode of the fourth transistor 104, anda gate electrode of the sixth transistor 106 is electrically connectedto the fifth input terminal 25. A first electrode of the seventhtransistor 107 is electrically connected to the fifth power supply line35, a second electrode of the seventh transistor 107 is electricallyconnected to the gate electrode of the second transistor 102 and thegate electrode of the fourth transistor 104, and a gate electrode of theseventh transistor 107 is electrically connected to the sixth inputterminal 26. A first electrode of the eighth transistor 108 iselectrically connected to the fifth power supply line 35, a secondelectrode of the eighth transistor 108 is electrically connected to asecond electrode of the ninth transistor 109, and a gate electrode ofthe eighth transistor 108 is electrically connected to the second inputterminal 22. A first electrode of the ninth transistor 109 iselectrically connected to the gate electrode of the second transistor102 and the gate electrode of the fourth transistor 104, and a gateelectrode of the ninth transistor 109 is electrically connected to thethird input terminal 23. A first electrode of the first capacitor 111 iselectrically connected to the sixth power supply line 36, and a secondelectrode of the first capacitor 111 is electrically connected to thegate electrode of the second transistor 102 and the gate electrode ofthe fourth transistor 104. A first electrode of the second capacitor 112is electrically connected to the output terminal 27, and the secondelectrode of the second capacitor 112 is electrically connected to thesecond electrode of the first transistor 101 and the gate electrode ofthe third transistor 103.

In FIG. 1C, a connection point of the second electrode of the firsttransistor 101, the second electrode of the second transistor 102, thegate electrode of the third transistor 103, and the second electrode ofthe second capacitor 112 is referred to as a node A. In addition, aconnection point of the gate electrode of the second transistor 102, thegate electrode of the fourth transistor 104, the second electrode of thefifth transistor 105, the second electrode of the sixth transistor 106,the second electrode of the seventh transistor 107, the first electrodeof the ninth transistor 109, and the second electrode of the firstcapacitor 111 is referred to as a node B. Further, a connection point ofthe second electrode of the third transistor 103, the second electrodeof the fourth transistor 104, the first electrode of the secondcapacitor 112, and the output terminal 27 is referred to as a node C.

Next, operation of the shift register shown in FIGS. 1A to 1C isdescribed with reference to FIG. 2, FIGS. 3A to 3D, and FIGS. 4A to 4D.Specifically, description is made by dividing a period of a timing chartof FIG. 2 into a first period 51, a second period 52, a third period 53,a fourth period 54, and a fifth period 55. Note that in the followingdescription, the first to ninth transistors 101 to 109 are N-channelthin film transistors, and they are in a conductive state when voltage(Vgs) between the gate and the source exceeds a threshold voltage (Vth).

In addition, here, an output of the second pulse output circuit 10 _(—2)is described. The first input terminal 21 of the second pulse outputcircuit 10 _(—2) is electrically connected to the second signal line 12which supplies the second clock signal (CK2), the second input terminal22 of the second pulse output circuit 10 _(—2) is electrically connectedto the third signal line 13 which supplies the third clock signal (CK3),and the third input terminal 23 of the second pulse output circuit 10_(—2) is electrically connected to the fourth signal line 14 whichsupplies the fourth clock signal (CK4).

Note that a potential (VDD) of V1 is supplied to the first power supplyline 31 and the fifth power supply line 35, and a potential (VSS) of V2is supplied to the second to fourth power supply lines 32 to 34 and thesixth power supply line 36, where V1>V2 is satisfied. In addition,although the first to fourth clock signals (CK1) to (CK4) are signalswhich alternate between an H level signal and an L level signal at aregular interval, a potential is VDD when the clock signal is at an Hlevel, and a potential is VSS when the clock signal is at an L level. Inaddition, here, VSS=0 is satisfied for simplification of explanation;however, the present invention is not limited thereto.

In the first period 51, the second start pulse (SP2) becomes an H level,and the first transistor 101 and the fifth transistor 105 which areelectrically connected to the fourth input terminal 24 of the secondpulse output circuit 10 _(—2) are turned on. Since the third clocksignal (CK3) and the fourth clock signal (CK4) are at an H level, theeighth transistor 108 and the ninth transistor 109 are also turned on(see FIG. 3A).

At this time, since the first transistor 101 is turned on, a potentialof the node A increases. In addition, although a direct tunnelingcurrent flows between the fifth power supply line 35 and the fourthpower supply line 34, a potential of the node B is controlled so thatthe second transistor 102 is turned off by adjusting the size of thetransistor. For example, an off state of the second transistor 102 isrealized in such a way that a channel width (a channel width in adirection perpendicular to a direction along which a carrier flows in asource region and a drain region) of the fifth transistor 105 is longerthan that of the eighth transistor 108 or the ninth transistor 109.

In the second period 52, an H level signal is outputted from the outputterminal 27 (OUT (1)) of the first pulse output circuit 10 _(—1), andthe sixth transistor 106 which is electrically connected to the fifthinput terminal 25 of the second pulse output circuit 10 _(—2) is turnedon. In addition, the third clock signal (CK3) becomes an L level, andthe eighth transistor 108 is turned off; therefore, a direct tunnelingcurrent which is seen in the first period 51 vanishes (see FIG. 3B).

At this time, the second electrode of the first transistor 101 functionsas a source electrode, and the potential of the node A is a value inwhich a threshold voltage of the first transistor 101 is extracted froma potential of the first power supply line 31; therefore, V1−Vth101(Vth101 is the threshold voltage of the first transistor 101) isobtained. Accordingly, the first transistor 101 is turned off, and thenode A is in a floating state while holding V1−Vth101.

Here, a potential of the gate electrode of the third transistor 103becomes V1−Vth101. When a voltage between the gate and the source of thethird transistor 103 exceeds the threshold value thereof, that is,(V1−Vth101−V2)>Vth103 (Vth103 is a threshold voltage of the thirdtransistor 103) is satisfied, the third transistor 103 is turned on.

In the third period 53, the second start pulse (SP2) becomes an L level,and the first transistor 101 and the fifth transistor 105 are turnedoff. In addition, the second clock signal (CK2) becomes an H level, andan H level signal is supplied to the first electrode of the thirdtransistor 103 which is electrically connected to the first inputterminal 21 (see FIG. 3C).

Here, since the third transistor 103 is turned on, current is generatedbetween the source and the drain, a potential of the node C (the outputterminal 27 (OUT(2))). namely, a potential of the second electrode (inthis case, the source electrode) of the third transistor 103 begins toincrease. There is capacitive coupling due to the second capacitor 112between the gate and the source of the third transistor 103, and withthe increase in the potential of the node C, a potential of the gateelectrode of the third transistor 103 which is in a floating stateincreases (bootstrap operation). Ultimately, the potential of the gateelectrode of the third transistor 103 is higher than VI+Vthl03, and thepotential of the node C is equal to VI.

Note that this bootstrap operation is performed by providing the secondcapacitor 112 between the gate electrode and the second electrode of thethird transistor 103; however, the bootstrap operation may be performedwith capacitive coupling of channel capacitance of the third transistor103 and capacitive coupling of parasitic capacitance between the gateelectrode and the second electrode of the third transistor 103, withoutproviding the second capacitor 112.

At this time, since the output terminal 27 (OUT (1)) of the first pulseoutput circuit 10 _(—1) is at an H level, the sixth transistor 106 isturned on, and the node B is held at an L level. According, when thepotential of the node C rises from an L level to an H level, malfunctiondue to capacitive coupling of the node B and the node C can besuppressed.

Then, in the latter half of the third period 53, the output terminal 27(OUT (1)) of the first pulse output circuit 10 _(—1) becomes an L level,and the sixth transistor 106 is turned off, whereby the node B is placedin a floating state. In addition, the third clock signal (CK3) becomesan H level, and the eighth transistor 108 is turned on (see FIG. 3D).

In the fourth period 54, the output terminal 27 (OUT (4)) of the fourthpulse output circuit 10 _(—4) becomes an H level, and the input terminal26 of the second pulse output circuit 10 _(—2) which is electricallyconnected to the output terminal 27 of the fourth pulse output circuit10 _(—4) becomes an H level, whereby the seventh transistor 107 isturned on, and the node B also becomes an H level. Accordingly, thesecond transistor 102 and the fourth transistor 104 are turned on andthe third transistor 103 is turned off, so that the output terminal 27(OUT (2)) becomes an L level. In addition, the fourth clock signal (CK4)becomes an H level, and the ninth transistor 109 is turned on (see FIG.4A).

Then, in the latter half of the fourth period 54, the third clock signal(CK3) becomes an L level, and the eighth transistor 108 is turned off(see FIG. 4B).

In the fifth period 55, the output terminal 27 (OUT (4)) of the fourthpulse output circuit 10 _(—4) becomes an L level, the seventh transistor107 is turned off, and the node B is in a floating state while holdingan H level. Accordingly, the second transistor 102 and the fourthtransistor 104 continue to be an on state (see FIG. 4C).

Then, in a certain period (when both the third clock signal (CK3) andthe fourth clock signal (CK4) are at an H level) of the fifth period 55,the eighth transistor 108 and the ninth transistor 109 are turned on,and an H level signal is regularly supplied to the node B (see FIG. 4D).

In this way, in a period during which the potential of the outputterminal 27 is held at an L level, an H level signal is regularlysupplied to the node B; therefore, malfunction of a pulse output circuitcan be suppressed. In addition, by regularly turning on or off theeighth transistor 108 and the ninth transistor 109, a shift of athreshold value of the transistor can be decreased.

In addition, in the fifth period 55, while an H level signal is notsupplied from the fifth power supply line 35 to the node B, thepotential of the node B may be decreased due to the off-current of thefifth transistor 105 and the sixth transistor 106 in some cases.However, since the first capacitor 111 is electrically connected to thenode B, decrease in the potential of the node B can be mitigated.

Note that, in this embodiment mode, the case where the fifth powersupply line 35 is set at the same potential (VDD) of V1 as the firstpower supply line 31 is shown; however, the fifth power supply line 35may be set lower than the first power supply line 31 (V1>V35>V2 issatisfied, and V35 is a potential of the fifth power supply line 35). Asa result of this, the potential of the gate electrode of the secondtransistor 102 and the potential of the gate electrode of the fourthtransistor 104 can be suppressed, the shift of the threshold value ofthe second transistor 102 and the shift of the threshold value of thefourth transistor 104 are reduced, whereby deterioration can besuppressed.

In addition, the shift register described in this embodiment mode uses adriving method in which a pulse outputted from the m-th pulse outputcircuit overlaps half (½ period) of a pulse outputted from the (m+1)thpulse output circuit, as shown in FIG. 5A. This can make time to chargein a wiring about twice as long as that in a driving method in which apulse outputted from the m-th pulse output circuit does not overlap apulse outputted from the (m+1)th pulse output circuit in a conventionalshift register (see FIG. 5B). In this way, by using a driving method inwhich a pulse outputted from the m-th pulse output circuit overlaps half(½ period) of a pulse outputted from the (m+1)th pulse output circuit,the present invention can provide a pulse output circuit which canwithstand large load and operate at high frequency. In addition, anoperating condition of a pulse output circuit can be improved. Inparticular, it is very effective to use the driving method shown in FIG.5A for a thin film transistor using amorphous silicon of which electriccharacteristics are inferior.

Note that the shift register and the pulse output circuit shown in thisembodiment mode can be combined with any structure of a shift registerand a pulse output circuit shown in other embodiment modes in thisspecification. Also, the present invention in this embodiment mode canbe also applied to a semiconductor device. A semiconductor device inthis specification means a device that can function by utilizing thesemiconductor characteristics.

(Embodiment Mode 2)

In this embodiment mode, structures of a shift register and a pulseoutput circuit which are different from those in the above embodimentmode will be described with reference to drawings.

A shift register shown in this embodiment mode includes the first ton-th pulse output circuits 10 _(—1) to 10 _(—n) (n≧3) and the first tofourth signal lines 11 to 14 each of which outputs a clock signal (seeFIG. 6A). In addition, each of the first to n-th pulse output circuits10 _(—1) to 10 _(—n) includes the first input terminal 21, the secondinput terminal 22, the third input terminal 23, the fourth inputterminal 24, the fifth input terminal 25, the sixth input terminal 26,the first output terminal 27, and a second output terminal 28 (see FIG.6B). Note that the shift register in this embodiment mode has astructure in which the second output terminal 28 is added to the pulseoutput circuit described in Embodiment Mode 1.

The first input terminal 21, the second input terminal 22, and the thirdinput terminal 23 are electrically connected to any of the first tofourth signal lines 11 to 14. In the m-th pulse output circuit (m≧3) ofthe shift register shown in this embodiment mode, the fourth inputterminal 24 of the m-th pulse output circuit is electrically connectedto the first output terminal 27 of the (m−2)th pulse output circuit andthe fifth input terminal 25 of the (m−1)th pulse output circuit. Thefifth input terminal 25 of the m-th pulse output circuit is electricallyconnected to the first output terminal 27 of the (m−1)th pulse outputcircuit and the fourth input terminal 24 of the (m+1)th pulse outputcircuit. The sixth input terminal 26 of the m-th pulse output circuit iselectrically connected to the first output terminal 27 of the (m+2)thpulse output circuit. The first output terminal 27 of the m-th pulseoutput circuit is electrically connected to the sixth input terminal 26of the (m−2)th pulse output circuit, the fifth input terminal 25 of the(m+1)th pulse output circuit, and the fourth input terminal 24 of the(m+2)th pulse output circuit, and the second output terminal 28 of them-th pulse output circuit outputs a signal to OUT(m).

That is, the shift register shown in this embodiment mode is providedwith the first output terminal 27 and the second output terminal 28 andhas a structure in which an output terminal for outputting a signal toanother pulse output circuit and another output terminal for outputtinga signal to outside are provided.

Next, a specific structure of each of the first to n-th pulse outputcircuits 10 _(—1) to 10 _(—n) shown in this embodiment mode will bedescribed.

Each of the first to n-th pulse output circuits 10 _(—1) to 10 _(—n)includes the first to ninth transistors 101 to 109, tenth to thirteenthtransistors 201 to 204, the first capacitor 111, the second capacitor112, and a third capacitor 211 (see FIG. 6C). The pulse output circuitshown in this embodiment mode has a structure in which the tenth tothirteenth transistors 201 to 204 and the third capacitor 211 are addedto the pulse output circuit described in Embodiment Mode 1. Further,signals are supplied to the transistors from the second output terminal28 and seventh to ninth power supply lines 37 to 39, in addition to thefirst to sixth input terminals 21 to 26, the first output terminal 27,and the first to sixth power supply lines 31 to 36 which are describedin Embodiment Mode 1.

A first electrode of the tenth transistor 201 is electrically connectedto the first input terminal 21, a second electrode of the tenthtransistor 201 is electrically connected to the second output terminal28, and a gate electrode of the tenth transistor 201 is electricallyconnected to the second electrode of the first transistor 101. A firstelectrode of the eleventh transistor 202 is electrically connected tothe eighth power supply line 38, a second electrode of the eleventhtransistor 202 is electrically connected to the second output terminal28, and the gate electrode of the eleventh transistor 202 iselectrically connected to the gate electrode of the second transistor102 and the gate electrode of the fourth transistor 104. A firstelectrode of the twelfth transistor 203 is electrically connected to theninth power supply line 39, a second electrode of the twelfth transistor203 is electrically connected to the second output terminal 28, and agate electrode of the twelfth transistor 203 is electrically connectedto a gate electrode of the ninth transistor 109. A first electrode ofthe thirteenth transistor 204 is electrically connected to the seventhpower supply line 37, a second electrode of the thirteenth transistor204 is electrically connected to the first output terminal 27, and agate electrode of the thirteenth transistor 204 is electricallyconnected to the gate electrode of the ninth transistor 109. A firstelectrode of the third capacitor 211 is electrically connected to thesecond output terminal 28, and a second electrode of the third capacitor211 is electrically connected to the second electrode of the firsttransistor 101 and the gate electrode of the tenth transistor 201.

In addition, a potential (VSS) of V2 can be supplied to the seventh toninth power supply lines 37 to 39, similarly to the second to fourthpower supply lines 32 to 34 and the sixth power supply line 36.

The first output terminal 27 and the second output terminal 28 areprovided so that the same signal is outputted, the tenth transistor 201corresponds to the third transistor 103, and the eleventh transistor 202corresponds to the fourth transistor 104. That is, the tenth transistor201 performs bootstrap operation similarly to the third transistor 103.Note that the bootstrap operation of the tenth transistor 201 isperformed by providing the third capacitor 211 between the gateelectrode and the second electrode of the tenth transistor 201; however,the bootstrap operation may be performed with capacitive coupling ofchannel capacitance of the tenth transistor 201 and capacitive couplingof parasitic capacitance between the gate electrode and the secondelectrode of the tenth transistor 201, without providing the thirdcapacitor 211.

The twelfth transistor 203 and the thirteenth transistor 204 are used soas to shorten fall time of a potential of a scan line. When the twelfthtransistor 203 and the thirteenth transistor 204 can sufficientlyshorten the fall time of the potential of the scan line, the fourthtransistor 104 and the eleventh transistor 202 do not necessarilyshorten the fall time of the potential of the scan line. Therefore, thepotential of the fifth power supply line 35 can be set lower than apower source of the first power supply line 31, which can reducethreshold shifts of the fourth transistor 104, the eleventh transistor202, and the second transistor 102.

Note that the shift register and the pulse output circuit shown in thisembodiment mode can be combined with any structure of a shift registerand a pulse output circuit shown in other embodiment modes in thisspecification. Also, the present invention in this embodiment mode canbe also applied to a semiconductor device.

(Embodiment Mode 3)

In this embodiment mode, structures of a shift register and a pulseoutput circuit which are different from those in the above embodimentmodes will be described.

In the structures described in Embodiment Modes 1 and 2, the examples inwhich all of the circuits are formed using N-channel thin filmtransistors are shown; however, a similar structure may be used in whichonly P-channel thin film transistors are used in terms of using unipolarthin film transistors. Although not shown in particular, in FIG. 1C orFIG. 6C, connection of the transistors is the same, and high and lowlevel potentials of a power source line may be inverted to the casesdescribed in Embodiment Modes 1 and 2. In addition, a structure may beused in which H level signals to be inputted and L level signals to beinputted are all inverted and inputted. Note that the present inventionin this embodiment mode can be also applied to a semiconductor device.

(Embodiment Mode 4)

A structure in which a display device is provided with the shiftregister described in the above embodiment modes will be described withreference to drawings.

In FIG. 9A, a display device includes a pixel portion 1102 in which aplurality of pixels 1101 is arranged in matrix over a substrate 1107,and includes a signal line driver circuit 1103, a first scan line drivercircuit 1104, and a second scan line driver circuit 1105 at theperiphery of the pixel portion 1102. Signals are supplied from outsideto these driver circuits through an FPC 1106.

In FIG. 9B, the structure of the first scan line driver circuit 1104 andthe second scan line driver circuit 1105 is shown. Each of the scan linedriver circuits 1104 and 1105 includes a shift register 1114 and abuffer 1115. In addition, in FIG. 9C, a structure of the signal linedriver circuit 1103 is shown. The signal line driver circuit 1103includes a shift register 1111, a first latch circuit 1112, a secondlatch circuit 1113, and a buffer 1117.

A circuit which operates as the shift register described in thisembodiment mode can be applied to the circuit of the shift register 1111and the circuit of the shift register 1114. By using the circuit whichoperates as the shift register described in the above embodiment modes,the circuit which operates as the shift register can be operated at highfrequency even when the circuit which operates as the shift register isprovided by using a thin film transistor which uses amorphous silicon.

Note that the structures of the scan line driver circuit and the signalline driver circuit are not limited to the structures shown in FIGS. 9Ato 9C, and for example, a sampling circuit, a level shifter, or the likemay be provided. Besides the above driver circuits, a circuit such as aCPU or a controller may be formed on the substrate 1107, which isparticularly advantageous to a portable terminal and the like becausethe number of external circuits (IC) to be connected decreases andfurther reduction in weight and thickness can be achieved.

Note that the display device shown in this embodiment mode can becombined with any structure of a shift register, a pulse output circuit,or a display device shown in other embodiment modes in thisspecification.

(Embodiment Mode 5)

In this embodiment mode, a structure of a display panel used for thedisplay device described in Embodiment Mode 4 will be described withreference to drawings.

First, a display panel applicable to the display device is describedwith reference to FIGS. 10A and 10B. Note that FIG. 10A is a top viewshowing a display panel, and FIG. 10B is a cross-sectional view of FIG.10A taken along line A-A′. The display panel includes a signal linedriver circuit 3601, a pixel portion 3602, a second scan line drivercircuit 3603, and a first scan line driver circuit 3606 which areindicated by dotted lines. It also includes a sealing substrate 3604 anda sealant 3605, and a portion surrounded by the sealant 3605 is a space3607.

Note that a wiring 3608 is a wiring for transmitting a signal to beinputted to the second scan line driver circuit 3603, the first scanline driver circuit 3606, and the signal line driver circuit 3601 andreceives a video signal, a clock signal, a start signal, and the likethrough an FPC (Flexible Printed Circuit) 3609 that serves as anexternal input terminal. An IC chip (a semiconductor chip provided witha memory circuit, a buffer circuit, or the like) 3618 and an IC chip3619 are mounted by COG (Chip On Glass) or the like at the junction ofthe FPC 3609 and the display panel. Note that only the FPC is shownhere; however, a printed wiring board (PWB) may be attached to the FPC.The display device in this specification includes not only a displaypanel itself but also a display panel with an FPC or a PWB attachedthereto. In addition, it also includes a display panel on which an ICchip or the like is mounted.

Next, a cross-sectional structure is described with reference to FIG.10B. The pixel portion 3602 and its peripheral driver circuits (thesecond scan line driver circuit 3603, the first scan line driver circuit3606, and the signal line driver circuit 3601) are formed over asubstrate 3610; here, the signal line driver circuit 3601 and the pixelportion 3602 are shown.

Note that as the signal line driver circuit 3601, a CMOS circuit isformed using an N-channel TFT 3620 and a P-channel TFT 3621. In thisembodiment mode, the display panel in which the peripheral drivercircuits are formed over the same substrate is described; however, thepresent invention is not limited to this. All or part of the peripheraldriver circuits may be formed on an IC chip or the like and mounted byCOG or the like.

The pixel portion 3602 includes a plurality of circuits each forming apixel which includes a switching TFT 3611 and a driving TFT 3612. Notethat a source electrode of the driving TFT 3612 is electricallyconnected to a first electrode 3613. An insulator 3614 is formed tocover end portions of the first electrode 3613. Here, a positive typephotosensitive acrylic resin film is used.

The insulator 3614 is formed to have a curved surface with a curvatureat an upper end portion or a lower end portion thereof in order to makethe coverage favorable. For example, in the case of using positive typephotosensitive acrylic as a material of the insulator 3614, theinsulator 3614 is preferably formed to have a curved surface with acurvature radius (0.2 μm to 3 μm) only at the upper end portion. Eithera negative type which becomes insoluble in an etchant by lightirradiation or a positive type which becomes soluble in an etchant bylight irradiation can be used as the insulator 3614.

A layer 3616 containing an organic compound and a second electrode 3617are formed over the first electrode 3613. Here, a material having a highwork function is preferably used as a material used for the firstelectrode 3613 which functions as an anode. For example, the firstelectrode 3613 can be formed using a single-layer film such as an ITO(Indium Tin Oxide) film, an indium zinc oxide (IZO) film, a titaniumnitride film, a chromium film, a tungsten film, a Zn film, or a Pt film;a stacked layer of a titanium nitride film and a film containingaluminum as its main component; a three-layer structure of a titaniumnitride film, a film containing aluminum as its main component, and atitanium nitride film; or the like. When the first electrode 3613 has astacked structure, it can have low resistance as a wiring and form afavorable ohmic contact. Further, the first electrode can function as ananode.

In addition, the layer 3616 containing an organic compound is formed byan evaporation method using an evaporation mask or an ink-jet method. Ametal complex belonging to Group 4 of the Periodic Table is used forpart of the layer 3616 containing an organic compound, and besides, amaterial which can be used in combination may be either a low molecularmaterial or a high molecular material. In addition, as a material usedfor the layer containing an organic compound, a single layer or astacked layer of an organic compound is often used generally. Inaddition, this embodiment mode also includes a structure in which aninorganic compound is used for part of the film formed of an organiccompound. Moreover, a known triplet material can also be used.

As a material used for the second electrode (cathode) 3617 which isformed over the layer 3616 containing an organic compound, a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or calcium nitride) may be used. In the casewhere light generated in the layer 3616 containing an organic compoundis transmitted through the second electrode 3617, a stacked layer of ametal thin film with a thin thickness and a transparent conductive film(ITO (Indium Tin Oxide)), an alloy of indium oxide and zinc oxide(In₂O₃—ZnO), zinc oxide (ZnO), or the like) is preferably used as thesecond electrode (cathode) 3617.

By attaching the sealing substrate 3604 to the substrate 3610 with thesealant 3605, a structure is obtained in which a display element 3622 isprovided in the space 3607 surrounded by the substrate 3610, the sealingsubstrate 3604, and the sealant 3605. Note that there is also a casewhere the space 3607 is filled with the sealant 3605 as well as an inertgas (such as nitrogen or argon).

Note that an epoxy-based resin is preferably used as the sealant 3605.The material preferably allows as little moisture and oxygen as possibleto penetrate. As the sealing substrate 3604, a plastic substrate formedof FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride),polyester, acrylic, or the like can be used besides a glass substrate ora quartz substrate.

The display panel can be obtained as described above.

As shown in FIGS. 10A and 10B, the signal line driver circuit 3601, thepixel portion 3602, the second scan line driver circuit 3603, and thefirst scan line driver circuit 3606 are formed over the same substrate,and thereby, reduction in cost of the display device can be realized.

Note that the structure of the display panel is not limited to thestructure shown in FIG. 10A, in which the signal line driver circuit3601, the pixel portion 3602, the second scan line driver circuit 3603,and the first scan line driver circuit 3606 are formed over the samesubstrate, and a signal line driver circuit 4201 shown in FIG. 11A,which corresponds to the signal line driver circuit 3601 may be formedover an IC chip and mounted on the display panel by COG or the like.Note that a substrate 4200, a pixel portion 4202, a second scan linedriver circuit 4203, a first scan line driver circuit 4204, an FPC 4205,an IC chip 4206, an IC chip 4207, a sealing substrate 4208, and asealant 4209 of FIG. 11A correspond to the substrate 3610, the pixelportion 3602, the second scan line driver circuit 3603, the first scanline driver circuit 3606, the FPC 3609, the IC chip 3618, the IC chip3619, the sealing substrate 3604, and the sealant 3605 of FIG. 10A,respectively.

That is, only the signal line driver circuit of which high speedoperation is required among the driver circuits is formed into an ICchip by using a CMOS or the like, and thereby, lower power consumptionis realized. Further, when a semiconductor chip formed of a siliconwafer or the like is used as the IC chip, higher speed operation andlower power consumption can be achieved.

Cost reduction can be realized by forming the first scan line drivercircuit 4203 and the second scan line driver circuit 4204 each providedwith the shift register described in the above embodiment modes, and thepixel portion 4202 over the same substrate.

As described above, cost reduction of a high-definition display devicecan be realized. Further, by mounting an IC chip including a functionalcircuit (memory or buffer) at a connection portion of the FPC 4205 andthe substrate 4200, a substrate area can be effectively used.

Further, a signal line driver circuit 4211, a second scan line drivercircuit 4214, and a first scan line driver circuit 4213 in FIG. 11Bwhich correspond to the signal line driver circuit 3601, the second scanline driver circuit 3603, and the first scan line driver circuit 3606 inFIG. 10A may be formed over an IC chip and mounted on a display panel byCOG or the like. In this case, further reduction in power consumption ofa high-definition display device can be realized. Accordingly, in orderto obtain a display device with less power consumption, polysilicon ispreferably used for semiconductor layers of transistors used in thepixel portion. Note that a substrate 4210, a pixel portion 4212, an FPC4215, an IC chip 4216, an IC chip 4217, a sealing substrate 4218, asealant 4219 of FIG. 11B correspond to the substrate 3610, the pixelportion 3602, the FPC 3609, the IC chip 3618, the IC chip 3619, thesealing substrate 3604, and the sealant 3605 of FIG. 10A, respectively.

In addition, when amorphous silicon is used for semiconductor layers oftransistors in the pixel portion 4212, cost reduction can be realized.Moreover, a large display panel can be manufactured as well.

Furthermore, an example of a display element applicable to the displayelement 3622 is shown in FIGS. 15A and 15B. That is, a structure of thedisplay element applicable to the pixel described in the aboveembodiment mode is described with reference to FIGS. 15A and 15B.

The display element of FIG. 15A has an element structure in which ananode 4402, a hole injecting layer 4403 formed of a hole injectingmaterial, a hole transporting layer 4404 formed of a hole transportingmaterial, a light emitting layer 4405, an electron transporting layer4406 formed of an electron transporting material, an electron injectinglayer 4407 formed of an electron injecting material, and a cathode 4408are stacked over a substrate 4401. Here, the light emitting layer 4405may be formed of only one kind of a light emitting material; however, itmay be formed of two or more kinds of materials. In addition, an elementstructure of the present invention is not limited to this structure.

In addition to the stacked structure of respective functional layersshown in FIGS. 15A and 15B, there is a wide range of variation inelement structure, such as an element using a high molecular compound ora high-efficiency element in which a light emitting layer is formedusing a triplet light emitting material that emits light from a tripletexcited state. In addition, the element structure of the presentinvention is also applicable to a white display element realized bycontrolling a carrier recombination region with a hole blocking layer todivide a light emitting region into two regions, or the like.

In a manufacturing method of the element of the present invention shownin FIG. 15A, first, a hole injecting material, a hole transportingmaterial, and a light emitting material are evaporated in this orderover the substrate 4401 provided with the anode 4402 (ITO). Then, anelectron transporting material and an electron injecting material areevaporated, and finally, the cathode 4408 is formed by evaporation.

Next, suitable materials for the hole injecting material, the holetransporting material, the electron transporting material, the electroninjecting material, and the light emitting material are listed below.

As the hole injecting material, a porphyrin compound, phthalocyanine(hereinafter referred to as “H₂Pc”), copper phthalocyanine (hereinafterreferred to as “CuPc”), or the like is effective among organiccompounds. In addition, a material which has a smaller value of anionization potential than that of the hole transporting material to beused and has a hole transporting function can also be used as the holeinjecting material. There is also a chemically-doped conductive highmolecular compound, which includes polyethylenedioxythiophene(hereinafter referred to as “PEDOT”) doped with polystyrene sulfonate(hereinafter referred to as “PSS”), polyaniline, and the like. Inaddition, an insulating high molecular compound is also effective inplanarization of the anode, and polyimide (hereinafter referred to as“PI”) is often used. Further, an inorganic compound is also used, whichincludes an ultrathin film of aluminum oxide (hereinafter referred to as“alumina”) as well as a thin film of metal such as gold or platinum.

A material that is most widely used as the hole transporting material isan aromatic amine-based compound (in other words, a compound having abond of benzene ring-nitrogen). A widely-used material includes4,4′-bis(diphenylamino)-biphenyl (hereinafter referred to as “TAD”), aderivative thereof such as4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (hereinafterreferred to as “TPD”) or4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as “α-NPD”), and besides, a star burst aromatic amine compound suchas 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (hereinafter referredto as “TDATA”) or4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(hereinafter referred to as “MTDATA”).

As the electron transporting material, a metal complex is often used,which includes a metal complex having a quinoline skeleton or abenzoquinoline skeleton such as Alq, BAlq,tris(4-methyl-8-quinolinolato)aluminum (hereinafter referred to as“Almq”), or bis(10-hydroxybenzo[h]-quinolinato)beryllium (hereinafterreferred to as “BeBq”), and besides, a metal complex having anoxazole-based or a thiazole-based ligand such asbis[2-(2-hydroxyphenyl)-benzoxazolato]zinc (hereinafter referred to as“Zn(BOX)₂”) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (hereinafterreferred to as “Zn(BTZ)₂”). Further, other than the metal complex, anoxadiazole derivative such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereinafterreferred to as “PBD”) or OXD-7, a triazole derivative such as TAZ or3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(hereinafter referred to as “p-EtTAZ”), and a phenanthroline derivativesuch as bathophenanthroline (hereinafter referred to as “BPhen”) or BCPhave an electron transporting property.

As the electron injecting material, the above-described electrontransporting materials can be used. In addition, an ultrathin film of aninsulator such as metal halide including calcium fluoride, lithiumfluoride, cesium fluoride, and the like, or alkali metal oxide includinglithium oxide, and the like is often used. Further, an alkali metalcomplex such as lithium acetyl acetonate (hereinafter referred to as“Li(acac)”) or 8-quinolinolato-lithium (hereinafter referred to as“Liq”) is also effective.

As the light emitting material, other than a metal complex such as Alq,Almq, BeBq, BAlq, Zn(BOX)₂, or Zn(BTZ)₂, various fluorescent pigmentsare effective. The fluorescent pigments include4,4′-bis(2,2-diphenyl-vinyl)-biphenyl which is blue,4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran whichis red-orange, and the like. In addition, a triplet light emittingmaterial is also possible, which is mainly a complex with platinum oriridium as central metal. As the triplet light emitting material,tris(2-phenylpyridine)iridium,bis(2-(4′-tryl)pyridinato-N,C^(2′))acetylacetonato iridium (hereinafterreferred to as “acacIr(tpy)₂”),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum, and the likeare known.

By combining the above-described materials that have respectivefunctions, a highly reliable display element can be manufactured.

In addition, a display element having layers stacked in reverse order ofthat in FIG. 15A can be used by changing the polarity of a drivingtransistor having the pixel structure described in the above embodimentmode so as to be an N-channel transistor, and reversing the magnitude ofa potential of an opposite electrode of a display element and apotential set to a power supply line. In other words, as shown in FIG.15B, an element structure is such that the cathode 4408, the electroninjecting layer 4407 formed of an electron injecting material, theelectron transporting layer 4406 formed of an electron transportingmaterial, the light emitting layer 4405, the hole transporting layer4404 formed of a hole transporting material, the hole injecting layer4403 formed of a hole injecting material, and the anode 4402 aresequentially stacked over the substrate 4401.

In addition, in order to extract light emission of a display element, atleast one of the anode and the cathode may be transparent. Then, a TFTand a display element are formed over a substrate. There are displayelements having a top emission structure in which light emission isextracted through the surface opposite to the substrate, having a bottomemission structure in which light emission is extracted through thesurface on the substrate side, and having a dual emission structure inwhich light emission is extracted through the surface opposite to thesubstrate and the surface on the substrate side. The pixel structuredescribed in the above embodiment mode can be applied to a displayelement having any of the emission structures.

A display element having the top emission structure is described withreference to FIG. 12A.

Over a substrate 4500, a driving TFT 4501 is formed with a base film4505 interposed therebetween, and a first electrode 4502 is formed incontact with a source electrode of the driving TFT 4501. A layer 4503containing an organic compound and a second electrode 4504 are formedthereover.

Note that the first electrode 4502 is an anode of the display element,and the second electrode 4504 is a cathode of the display element. Inother words, the display element is formed in a region where the layer4503 containing an organic compound is sandwiched between the firstelectrode 4502 and the second electrode 4504.

Here, the first electrode 4502 which functions as an anode is preferablyformed using a material having a high work function. For example, asingle-layer film such as a titanium nitride film, a chromium film, atungsten film, a Zn film, or a Pt film; a stacked layer of a titaniumnitride film and a film containing aluminum as its main component; athree-layer structure of a titanium nitride film, a film containingaluminum as its main component, and a titanium nitride film; or the likecan be used. Note that when the first electrode 4502 has a stackedstructure, it can have low resistance as a wiring, form a good ohmiccontact, and function as an anode. By using a light-reflective metalfilm, an anode which does not transmit light can be formed.

The second electrode 4504 which functions as a cathode is preferablyformed using a stacked layer of a metal thin film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or calcium nitride) and a transparent conductivefilm (ITO (Indium Tin Oxide), indium zinc oxide (IZO), zinc oxide (ZnO),or the like). By using the thin metal film and the transparentconductive film as described above, a cathode which can transmit lightcan be formed.

Thus, light of the display element can be extracted from a top surfaceas indicated by an arrow in FIG. 12A. In other words, in the case ofapplying the display element to the display panel shown in FIGS. 10A and10B, light is emitted toward the sealing substrate 3604 side. Therefore,when a display element having the top emission structure is used for thedisplay device, a substrate which transmits light is used as the sealingsubstrate 3604.

In addition, in the case of providing an optical film, the optical filmmay be provided over the sealing substrate 3604.

Next, a display element having the bottom emission structure isdescribed with reference to FIG. 12B. Description is made using the samereference numerals as those in FIG. 12A since a structure except for itsemission structure is identical.

Here, the first electrode 4502 which functions as an anode is preferablyformed using a material having a high work function. For example, atransparent conductive film such as an ITO (Indium Tin Oxide) film or anindium zinc oxide (IZO) film can be used. By using a transparentconductive film, an anode which can transmit light can be formed.

The second electrode 4504 which functions as a cathode can be formedusing a metal film formed of a material having a low work function (Al,Ag, Li, Ca, or an alloy thereof such as MgAg, MgIn, AlLi, CaF₂, orcalcium nitride). By using a light-reflective metal film as describedabove, a cathode which does not transmit light can be formed.

Thus, light of the display element can be extracted from a bottomsurface as indicated by an arrow in FIG. 12B. In other words, in thecase of applying the display element to the display panel shown in FIGS.10A and 10B, light is emitted toward the substrate 3610 side. Therefore,when the display element having the bottom emission structure is usedfor the display device, a substrate which transmits light is used as thesubstrate 3610.

In addition, in the case of providing an optical film, the optical filmmay be provided over the substrate 3610.

Next, a display element having the dual emission structure is describedwith reference to FIG. 12C. Description is made using the same referencenumerals as those in FIG. 12A since a structure except for its emissionstructure is identical.

Here, the first electrode 4502 which functions as an anode is preferablyformed using a material having a high work function. For example, atransparent conductive film such as an ITO (Indium Tin Oxide) film or anindium zinc oxide (IZO) film can be used. By using a transparentconductive film, an anode which can transmit light can be formed.

The second electrode 4504 which functions as a cathode is preferablyformed using a stacked layer of a metal thin film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or calcium nitride) and a transparent conductivefilm (ITO (Indium Tin Oxide), an alloy of indium oxide and zinc oxide(In₂O₃—ZnO), zinc oxide (ZnO), or the like). By using the thin metalfilm and the transparent conductive film as described above, a cathodewhich can transmit light can be formed.

Thus, light of the display element can be extracted from both surfacesas indicated by arrows in FIG. 12C. In other words, in the case ofapplying the display element to the display panel shown in FIGS. 10A and10B, light is emitted toward the substrate 3610 side and the sealingsubstrate 3604 side. Therefore, when the display element having the dualemission structure is used for the display device, substrates whichtransmit light are used as both the substrate 3610 and the sealingsubstrate 3604.

In addition, in the case of providing an optical film, the optical filmmay be provided over both the substrate 3610 and the sealing substrate3604.

In addition, the present invention can be applied to a display devicewhich achieves full-color display by using a white display element and acolor filter.

As shown in FIG. 13, for example, a structure can be formed in which abase film 4602 is formed over a substrate 4600, a driving TFT 4601 isformed thereover, and a first electrode 4603 is formed in contact with asource electrode of the driving TFT 4601. A layer 4604 containing anorganic compound and a second electrode 4605 are formed thereover.

Note that the first electrode 4603 is an anode of the display element,and the second electrode 4605 is a cathode of the display element. Inother words, the display element is formed in a region where the layer4604 containing an organic compound is sandwiched between the firstelectrode 4603 and the second electrode 4605. In the structure shown inFIG. 13, white light is emitted. A red color filter 4606R, a green colorfilter 4606Q and a blue color filter 4606B are provided above each ofthe display elements to achieve full-color display. In addition, a blackmatrix (also referred to as a “BM”) 4607 which separates these colorfilters is provided.

The above-described structures of the display element can be used incombination and can be appropriately used for the display device whichis operated by the pulse output circuit or the shift register of thepresent invention. Note that the structures of the display panels andthe display elements described above are merely examples, and needlessto say, another structure can also be used.

(Embodiment Mode 6)

The present invention can be applied to various electronic devices.Specifically, it can be applied to the driving of a display portion ofan electronic device. Examples of such an electronic device are asfollows: a camera such as a video camera or a digital camera, a goggletype display, a navigation system, a sound reproducing device (such as acar audio or an audio component), a computer, a game machine, a portableinformation terminal (such as a mobile computer, a mobile phone, aportable game machine, or an e-book reader), an image reproducing deviceprovided with a recording medium (specifically, a device which canreproduce a recording medium such as a digital versatile disc (DVD) andincludes a light emitting device capable of displaying images thereof),and the like.

FIG. 14A shows a light emitting device, which includes a chassis 6001, asupport 6002, a display portion 6003, speaker portions 6004, a videoinput terminal 6005, and the like. The display device of the presentinvention can be used for the display portion 6003. Note that the lightemitting device includes any light emitting devices used for displayinginformation, for example, for a personal computer, for TV broadcastreception, or for advertisement display. The shift register of thepresent invention is used to drive the display portion 6003, so thatpower consumption can be reduced.

FIG. 14B shows a camera, which includes a main body 6101, a displayportion 6102, an image receiving portion 6103, operation keys 6104, anexternal connection port 6105, a shutter button 6106, and the like. Theshift register of the present invention is used to drive the displayportion 6102, so that power consumption can be reduced.

FIG. 14C shows a computer, which includes a main body 6201, a chassis6202, a display portion 6203, a keyboard 6204, an external connectionport 6205, a pointing device 6206, and the like. The shift register ofthe present invention is used to drive the display portion 6203, so thatpower consumption can be reduced.

FIG. 14D shows a mobile computer, which includes a main body 6301, adisplay portion 6302, a switch 6303, operation keys 6304, an infraredport 6305, and the like. The shift register of the present invention isused to drive the display portion 6302, so that power consumption can bereduced.

FIG. 14E shows a portable image reproducing device provided with arecording medium (specifically, a DVD reproducing device), whichincludes a main body 6401, a chassis 6402, a display portion A 6403, adisplay portion B 6404, a recording medium (DVD or the like) readingportion 6405, an operation key 6406, a speaker portion 6407, and thelike. The display portion A 6403 mainly displays image information, andthe display portion B 6404 mainly displays character information. Theshift register of the present invention is used to drive the displayportion A 6403 and the display portion B 6404, so that power consumptioncan be reduced.

FIG. 14F shows a goggle type display, which includes a main body 6501, adisplay portion 6502, an arm portion 6503, and the like. The shiftregister of the present invention is used to drive the display portion6502, so that power consumption can be reduced.

FIG. 14G shows a video camera, which includes a main body 6601, adisplay portion 6602, a chassis 6603, an external connection port 6604,a remote control receiving portion 6605, an image receiving portion6606, a battery 6607, an audio input portion 6608, operation keys 6609,an eyepiece portion 6610, and the like. The shift register of thepresent invention is used to drive the display portion 6602, so thatpower consumption can be reduced.

FIG. 14H shows a mobile phone, which includes a main body 6701, achassis 6702, a display portion 6703, an audio input portion 6704, anaudio output portion 6705, an operation key 6706, an external connectionport 6707, an antenna 6708, and the like. The shift register of thepresent invention is used to drive the display portion 6703, so thatpower consumption can be reduced.

As described above, the present invention can be applied to variouselectronic devices.

This application is based on Japanese Patent Application serial No.2006-282931 filed in Japan Patent Office on Oct. 17, 2006, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A pulse output circuit comprising: first, second,third, fourth, and fifth transistors; first, second, third and fourthinput terminals; and an output terminal; wherein a first electrode ofthe first transistor is electrically connected to the first inputterminal, and a second electrode of the first transistor is electricallyconnected to the output terminal, wherein a first electrode of thesecond transistor is configured to be supplied with a first potential,and a second electrode of the second transistor is electricallyconnected to the output terminal, wherein a first electrode of the thirdtransistor is configured to be supplied with the first potential, asecond electrode of the third transistor is electrically connected to agate electrode of the second transistor, and a gate electrode of thethird transistor is electrically connected to the fourth input terminal,wherein a second electrode of the fourth transistor is electricallyconnected to a second electrode of the fifth transistor, and a gateelectrode of the fourth transistor is electrically connected to thesecond input terminal, and wherein a first electrode of the fifthtransistor is electrically connected to the gate electrode of the secondtransistor, and a gate electrode of the fifth transistor is electricallyconnected to the third input terminal.
 2. The pulse output circuitaccording to claim 1, wherein each of the first, second, third, fourth,and fifth transistors comprises silicon.
 3. The pulse output circuitaccording to claim 1, wherein each of the first, second, third, fourth,and fifth transistors comprises amorphous silicon.
 4. The pulse outputcircuit according to claim 1, wherein a channel width of the thirdtransistor is larger than a channel width of the fourth transistor and achannel width of the fifth transistor.
 5. The pulse output circuitaccording to claim 1, wherein the gate electrode of the secondtransistor is configured to be supplied with a voltage through thefourth transistor and the fifth transistor.
 6. The pulse output circuitaccording to claim 1, wherein a first electrode of the fourth transistoris electrically connected to a fifth power supply line.
 7. A displaydevice comprising: a pixel portion over a substrate; and a drivercircuit for driving the pixel portion, the driver circuit comprising anpulse output circuit which comprises: first, second, third, fourth, andfifth transistors; first, second, third and fourth input terminals; andan output terminal; wherein a first electrode of the first transistor iselectrically connected to the first input terminal, and a secondelectrode of the first transistor is electrically connected to theoutput terminal, wherein a first electrode of the second transistor isconfigured to be supplied with a first potential, and a second electrodeof the second transistor is electrically connected to the outputterminal, wherein a first electrode of the third transistor isconfigured to be supplied with the first potential, a second electrodeof the third transistor is electrically connected to a gate electrode ofthe second transistor, and a gate electrode of the third transistor iselectrically connected to the fourth input terminal, wherein a secondelectrode of the fourth transistor is electrically connected to a secondelectrode of the fifth transistor, and a gate electrode of the fourthtransistor is electrically connected to the second input terminal, andwherein a first electrode of the fifth transistor is electricallyconnected to the gate electrode of the second transistor, and a gateelectrode of the fifth transistor is electrically connected to the thirdinput terminal.
 8. The display device according to claim 7, wherein eachof the first, second, third, fourth, and fifth transistors comprisessilicon.
 9. The display device according to claim 7, wherein each of thefirst, second, third, fourth, and fifth transistors comprises amorphoussilicon.
 10. The display device according to claim 7, wherein a channelwidth of the third transistor is larger than a channel width of thefourth transistor and a channel width of the fifth transistor.
 11. Thedisplay device according to claim 7, wherein the gate electrode of thesecond transistor is configured to be supplied with a voltage throughthe fourth transistor and the fifth transistor.
 12. The display deviceaccording to claim 7, wherein a first electrode of the fourth transistoris electrically connected to a fifth power supply line.